Dental implants of this type are for use as the anchoring members of dental prosthesis. To this end, the dental implant is inserted into a bore-hole drilled into the bone tissue of a jaw bone (maxilla or mandible) at a site where the dental prosthesis is required by rotating the dental implant into the bore-hole. The convention in the art is for the circumferentially-oriented roughness on the dental implant to take the form of a screw thread and in this case the bore-hole will typically be (i) provided with internal threads in advance, or (ii) left un-tapped with the dental implant being provided with a self-tapping capacity, e.g. by the provision of one or more axially-extending cutting recesses or notches in the screw thread.
A superstructure having the prosthetic part of the prosthesis is then secured to the dental implant. The superstructure will typically consist of a spacer or transmucosal component which engages to the dental implant to bridge the gingiva overlying the maxilla or mandible at the dental implant site and the prosthetic part, e.g. a crown, bridge or denture, is then secured to the spacer. There are various other forms that the superstructure can take as is known in the art. For instance, the prosthetic part may be secured directly to the dental implant.
The long-term integrity of the prosthesis is highly dependent on the successful osseointegration of the dental implant with the bone tissue of the maxilla or mandible, that is to say, the remodelling of the bone tissue in the maxilla or mandible into direct apposition with the dental implant. A study on the factors which affect the osseointegration of dental implants was undertaken by Professor Per-Ingvar Branemark and co-workers and the results were published in a book entitled "Osseointegrated Implants in the Treatment of the Edentulous Jaw: Experience from a 10-Year Period", Almqvist & Wiskell International, Stockholm, Sweden, 1977. It was found by Branemark et al that successful osseointegration depends upon inter alia the use of biocompatible materials for the dental implant, for example titanium and alloys thereof, and the surgical procedure adopted, for example leaving the dental implant unloaded for several months before adding the superstructure.
Dental implants having a circumferentially-oriented roughness have some notable advantages in promoting successful osseointegration with the adjacent bone tissue, a major one being as a result of the fact that the main loads on the dental implant in the clinical situation are axial loads. These dental implants are very well suited to support axial loads and this may be particularly important in the initial stages of the osseointegration process in which it is important that the dental implant is fully stable and as immovable as possible in the bore-hole (primary fixation). One can consider this to be due to the bone tissue growing into the troughs between adjacent peaks of the circumferentially-oriented roughness on the dental implant.
In Applicant's prior International patent application publication WO94/07428 there is disclosed a dental implant consisting of a body which has a coronal end surface, an apical end surface and a generally cylindrical section which extends apically from a position in close proximity to the coronal end surface. The outer peripheral surface of the generally cylindrical section is presented by one or more screw threads each of height no more than 0.2 mm, so-called microthreads. The use of microthreads enables the dental implant to be both tapped and screwed into a bore-hole provided in a jaw bone.
It would be an advantage to provide a dental implant with a circumferentially-oriented roughness which commences close to the coronal end surface of the dental implant as in WO94/07428 but which has a trough-to-peak height greater than that of microthreads.